1. Field of the Invention
The present invention relates to a process for the alkylation of organic aromatic compounds. More particularly the invention relates to a process for the concurrent alkylation and distillation of reaction components (reactants and products) in a catalyst bed wherein the catalyst also serves as the distillation structure. More particularly the invention relates to a method of operating an aromatic alkylation process wherein the olefin is contained in a stream having "inert" aliphatic compounds therein and wherein the aromatic stream also contains aliphatic compounds.
2. Related Art
Ethyl benzene and cumene have traditionally been produced by the reaction of benzene and the respective olefin, i.e., ethylene and propylene in the presence of an acidic catalyst. In some known processes the catalyst is highly corrosive and has a relatively short life, e.g., AlCl.sub.3, H.sub.3 P0.sub.4 on clay, BF.sub.3 on alumina, and others require periodic regeneration, e.g., molecular sieves. The exothermicity of the reaction and the tendency to produce polysubstituted benzene require low benzene conversions per pass with large volume recycle in conventional processes.
Recently a new method of carrying out catalytic reactions has been developed, wherein the components of the reaction system are concurrently separable by distillation, using the catalyst structures as the distillation structures. Such systems are described variously in U.S. Pat. Nos. 4,215,011; 4,232,177; 4,242,530; 4,250,052; 4,302,356; and 4,307,254 commonly assigned herewith. Briefly, a structure described there is a cloth belt with a plurality of pockets spaced along the belt, which is then wound in a helix about a spacing material such as stainless steel knitted mesh. These units are then disposed in the distillation column reactor. In addition, commonly assigned U.S. Pat. No. 4,443,559 discloses a variety of catalyst structures for this use and is incorporated herein.
More recently the method has been applied to aromatic alkylation as in U.S. Pat. No. 4,849,569 and copending and commonly assigned application Ser. Nos. 07/122,485 and 07/264,844. As noted therein the olefin feed to the alkylation process often contains aliphatic compounds which have a boiling range in and around the specific olefin to be used in the reaction. These aliphatic compounds are inert and simply pass through the distillation column reactor. However, in the final separation of unreacted aromatic compound (which is usually recycled to the reactor as reflux) from the inerts, it has been found that such separation can require extensive capital investment in the form of additional distillation trays. Additionally, it has sometimes been found to be advantageous to include a second separate distillation column fixed bed reactor or fixed bed reactor to polish or finish the reaction of all the olefin with aromatic.
Advantages of the present invention include a better utilization of the aromatic compound and more complete reaction of the olefin.